Method of comminuting ammonium nitrate prills mixed with hydrocarbon



Feb. 21, 1967 s. HODGSON 3,3@5,4%14

METHOD OF COMMINUTING AMMONIUM NITRATE PRILLS MIXED WITH HYDROCARBONFiled March 18, 1964 INVENTOR.

Stanley Hodgson gmwm Agent United States Patent This invention relatesto explosive compositions and is a particularly directed to a method andapparatus for producing a highly effective explosive composition fromprilled ammonium nitrate and liquid hydrocarbon mixtures and the productproduced thereby.

Explosive compositions made from a mixture of prilled ammonium nitrateand a liquid hydrocarbon have been widely adopted and used by the miningindustry for primary blasting. Such mixtures are relatively inexpensivecompared to conventional explosives and provide results comparable tothose obtained with conventional nitroglycerine explosives. The ammoniumnitrate-liquid hydrocarbon mixtures can be quickly and readily loaded bypneumatic devices into small diameter blast holes used in undergroundmining operations and can be readily detonated by a primer charge. Goodrock fragmentation is obtained and toxic fumes are normally notexcessive.

In most mining operations, particularly in underground operations,secondary blasting also is frequently required and relied upon to breakchunks of rock and ore too large for normal handling and to releasematerial that has bridged or otherwise hung up in raises, chutes, stopesand the like mine passageways. Secondary breaking has been effected withammonium nitrate-liquid hydrocarbon mixtures by placing a suitablequantity of the mixture on or against the material to be broken andemploying a blasting cap and a booster charge such as dynamite todetonate the ammonium nitrate-liquid hydrocarbon mixture. Although theseprimer charges are generally satisfactory for detonating the ammoniumnitrate-liquid hydrocarbon mixture, they are relatively sensitive toimpact and heat and, therefore, are subject to the hazard of prematuredetonation.

There is some hazard, therefore, in manipulating and positioning aquantity of ammonium nitrate explosive mixture containing such primers,particularly if the material must be manually transported long distancesunder space-restricted conditions and/ or placed where rock falling ontoa prepared charge may initiate a premature detonation. In someinstances, the charge must be manipulated into a position or feet fromthe operator by means of bulldoze sticks and, under such conditions, thedanger of premature detonation becomes a serious hazard.

I have found that the above hazards can be substantially overcome bycomminuting the ammonium nitrateliquid hydrocarbon mixture to apredetermined size range whereby the resulting cornminuted ammoniumnitrateliquid hydrocarbon mixture is rendered detonable by a shortlength of detonating cord thus permitting the sub stitution ofdetonating cord for the dynamite or blasting cap primer. The combinationof the comminuted or pulverized ammonium nitrate-liquid hydrocarbonmixture with detonating cord is considerably less likely to detonateprematurely than the standard ammonium nitrate-liquid hydrocarbonmixture primed with dynamite and a blasting cap, while providing all theadvantageous characteristics of a highly effective explosive forsecondary breaking.

It is known that finely comminuted ammonium nitrate is more sensitivethan prilled uncomminuted material, and it has been proposed, asdisclosed in United States Patent No. 3,046,887 to Brinkley et al., touse particles as fine as 100 mesh admixed with 0.5% to 3.5% by weight ofhydrocarbon for a cap sensitive primer charge. The Brinkley et al.disclosure specifically teaches comminution of ammonium nitrate prillsbefore mixing the ammonium nitrate with oil to produce the desiredexplosive composition. My test work has shown that ammoniumnitrateliquid hydrocarbon explosive compositions produced from ammoniumnitrate prills comminuted prior to mixing with liquid hydrocarbon, e.g.,fuel oil, result in an unsatisfactory mixture which is diflicult tohandle and in which the ammonium nitrate particles are not uniformlycoated with oil and have not uniformly absorbed the oil.

I have discovered that by first mixing the prills or particles ofammonium nitrate with about 5 to 6% by weight of liquid hydrocarbon andthen pulverizing or otherwise comminuting the particles of the resultantmixture so that at least 60%, and preferably about of the particles areof a size less than 28-mesh (standard Tyler screen), a highly effectiveexplosive composition is produced. There is no need for subsequenttreatment such as oiling, screening or separation of particle sizes.This mixture can be completely detonated by a 12-inch length of 40-grainper foot detonating cord.

The pulverized mixture can be packaged ready for use in quantitiesweighing /2 pound to about 50 pounds or more, each package containing ashort length of detonating cord, for example, about 12 inches of40-grain Primacord. The mixture is similar in texture to dry snow. Ithas an angle of repose of substantially and therefore does not readilyspill from torn bags. It is cohesive; it will adhere to and retain thecontour of the rock against which it is placed or tamped; and it isreadily adaptable to placement in voids between rocks.

It is a primary object of the present invention to provide an explosivecomposition which will substantially overcome the hazards associatedwith secondary blasting and encountered with standard ammoniumnitrate-liquid hydrocarbon mixtures by obviating the need for dynamiteand/ or blasting cap primers.

It is another object of the present invention to provide an ammoniumnitrate-liquid hydrocarbon explosive composition having a highlyeffective detonating force.

A further object of the present invention is the provision of a methodand apparatus for efiiciently producing such an explosive compositionfrom conventional ammonium nitrate mixtures.

An understanding of these and other objects of the present invention andthe manner in which they can be attained will become apparent from thefollowing detailed description of the method and apparatus of theinvention, reference being had to the accompanying drawing in which:

FIGURE 1 is a perspective view of an apparatus employed in the method ofthe present invention;

FIGURE 2 is a side elevation, partly cut away, illustrating in moredetail a portion of the apparatus shown in FIGURE 1; and

FIGURE 3 is an exploded perspective of a component part employed in thepresent apparatus.

Like reference characters refer to like parts throughout the descriptionand the drawing.

One specific embodiment of the apparatus of the present invention asillustrated by the drawing comprises a support frame 10 having a collar11 adapted to receive flange 12 of cylindrical vessel 13 for rigidengagement therewith by means of a plurality of bolts 14. A hood 15having outwardly diverging side walls defining an enlarged upper section16 is in like manner secured to collar 11 by flange 17 so that said hoodis axially aligned with chamber 18 of vessel 13 making an air-tightconnection therewith. A pair of rectangular ports formed in the upperportion 16 of hood are covered by conventional dust filters 19fabricated from glass fiber, aluminum and the like filter materialsadapted to permit the passage of gases therethrough while restrainingthe flow of dust and other particles for reasons which will becomeapparent as the description proceeds.

The lowermost portion 21 of vessel 13 is adapted to receive a pliablecontainer such as a sack 22 removably fastened thereto by a ring support23 so that the sack is in communication with chamber 18. It will beevident that ring support 23 will provide an air-tight connectionbetween the sack 22 and vessel 13.

A baflle plate 25 is adapted to be disposed partially across chamber 18of vessel 13 at an angle of about 45 to the longitudinal axis of thevessel as illustrated most clearly in FIGURE 2. With reference now toFIGURE 3, it will be observed that vessel 13 preferably is fabricated intwo sections 26 and 27 having inclined opposed flanges 28 and 29 formedthereon or integrally'secured thereto by welding or the like means. Acentral plate 30 having a slot 31 formed therein adapted to slidablyreceive bafile plate 25 is disposed between flanges 28 and 23 and rigidly secured to the flanges by a plurality of bolts, not shown. Baffleplate 25 is slidably inserted into slot 31 and positioned for thedesired projection within chamber 18 by a cotter pin 33 adapted to beinserted into one of holes 34 formed in plate 25.

A tube 35 adapted to open into chamber 18 is rigidly affixed to sleeve36 by a threaded connection 37. Sleeve 36 is secured to the wall ofvessel 13 by a weld or the like connecting means so that thelongitudinal axis of sleeve 36 and tube 35 coaxial therewith is directedtowards a central portion of baffle plate 25 at an angle of about 75 tothe plane of said batfle plate. Tube 35 is connected with a conventionalpneumatic loader 38 having an air supply line 39 and an ammonium nitratesupply line 40 in communication with a source of ammonium nitrate prillsin container 41.

In the operation of this apparatus, air under about 90 p.s.i. pressuresupplied by line 39 flows through loader 38 into chamber 18 of vessel13. The flow of air through loader 38 creates a low pressure in ammoniumnitrate supply line 39 inducing the hydrocarbon treated prills incontainer 41 to flow through line 40 into loader 38 for entrainment withthe air flowing through tube 35. The prills are acceleratedsubstantially to the velocity of the air flowing through tube 35 andejected into chamber 18 for impingement at high velocity againststationary baffle plate 25. It will be evident that the air will passaround the lowermost end of baflle plate 25 by way of opening 42 formedbetween the end of plate 25 and the wall of vessel 13 up into hood 15and escape to the atmosphere through filters 19, carrying a smallportion of the finesized comminuted ammonium nitrate mixture into thehood.

To minimize the collection of dust on filters 19, the upper portion ofhood 15 is enlarged to reduce the upward velocity of air flowingtherethrough so that a portion of the comminuted material carriedthrough port 42 will settle out before reaching the filters. Also, avibrator, not shown, may be incorporated with the structure of theapparatus to shake dust from filters 19 and prevent a dust build-up.

The bulk of the comminuted material formed when the ammonium nitrateprills strike the baffle plate 25 is deflected downwardly in chamber 18and falls by gravity into container 22. It will be understood thatalthough the operation of the apparatus as illustrated is carried out asa batch operation, it can readily be converted to a continuousoperation.

The following example illustrates the apparatus, method and productproduced thereby according to the present invention. Vessel 13 wasformed from a steel tube having an inside diameter of about 8 inches.Hood 15, secured to the upper end of vessel 13, was covered with a pairof glass fiber filters. The lower opening of vessel 13 was closed with aheavy paper sack 22. Inlet tube 35, consisting of a inch diameter steelpipe about 10 inches long, was arranged substantially as illustrated inthe drawing. Baffle plate 25, formed from a steel plate, was disposedwithin chamber 18 so that a maximum gap of 4 inches existed between theend of plate 25 and the vessel wall, measured in the plane of thebaffle. The loader and feed tube were grounded by means of ground wiresto preclude a build-up of static electricity. Air supplied under apressure of psi. permitted comminution of a mixture of ammonium nitrateand liquid hydrocarbon at a rate of 20 pounds per mintue.

The ammonium nitrate-liquid hydrocarbon prill mixture supplied incontainer 41 was prepared according to the following procedure. Ammoniumnitrate prills in the size range of minus 10 plus 28-mesh (standardTyler screen) were conditioned in the usual manner, for example, bymixing with 1%, by weight, of diatomaceous earth or with 0.5%, byweight, of AC-lO (a mixture of 90% clay and 10% organic surfactant). Theconditioned prills were thoroughly mixed with about 5 /2 by weight, ofliquid hydrocarbon, such as No. 2 fuel oil. This mixture was projectedat high velocity against the stationary baffle as described hereinabove,thereby comminuting the ammonium nitrate prills so that at least 60% ofthe comminuted material passed a 28-mesh standard Tyler screen.

The treated ammonium nitrate-liquid hydrocarbon mixture was bagged toform a plurality of individual charges. To each charge a 12-inch lengthof 40-grain detonating cord, known in the trade as B-line Primacord, wasadded, the detonating cord being coiled and positioned centrally withinthe charge with one end of the cord projecting from the neck of the bag.Detonating tests conducted on a plurality of charges confirmed that thel2-inch length of detonating cord provided an adequate booster to ensurecomplete detonation of charges weighing from /2 to 50 pounds.

It is advisable to prepare the pulverized or comminuted mixture at thesite where it will he used, and only in the quantities required fordaily use. Prolonged storage can result in caking of the material.

The present invention provides a number of important advantages.Ammonium nitrate prills mixed with a predetermined amount of liquidhydrocarbon and treated according to the process of the inventionprovide an explosive composition which is more sensitive to detonation,while having a higher order detonating force, than standard ammoniumnitrate-liquid hydrocarbon explosive mixtures. A 40-grain detonatingcord is satisfactory for detonating charges of /2 to 50 pounds or morein weight, and the usual blasting cap or dynamite primer in the chargeis unnecessary, thus improving safety conditions. The comminutedmaterial is cohesive thereby permitting the use of charges which can bereadily placed on or against the object to be fractured. The explosivemixture can be quickly and inexpensively manufactured from standardstarting materials, i.e., ammonium nitrate prills conditioned with amaterial such as clay or diatomaceous earth, and a liquid hydrocarbonsuch as No. 2 fuel oil, diesel oil, Mentor 29 (an oil of relatively lowvolatility), and the like.

It will be understood, of course, that modifications can be made in thepreferred embodiment of the invention described and illustrated hereinwithout departing from the scope and purview of the appended claim.

What I claim as new and desire to protect by Letters Patent of theUnited States is:

In a method for the production of an improved explosive compositiondetonable with detonating cord from a mixture of conditioned ammoniumnitrate prills with about 5% to about 6% by weight of a liquidhydrocarbon, the steps of introducing particles of said mixture into astream of air, projecting said particles entrained in said ReferencesCited by the Examiner UNITED STATES PATENTS 1,614,314 1/1927 Murray etal. 24140 X 2,768,938 10/1956 Martin 241-40 X 2,991,946 7/1961 Croft241-40 2,992,912 7/1961 Hradel et al. 149-46 3,095,335 6/1963 McCloud etal. 14960 X 6 3,111,437 11/1963 Hino et al 149-46 3,184,169 5/1965Friedman et al 241-4O FOREIGN PATENTS 5 883,276 11/ 1961 Great Britain.

OTHER REFERENCES Bennington et al.: German application 1,143,135,printed Jan. 31, 1963.

CARL D. QUARFORTH, Primary Examiner.

LEON D. ROSDOL, BENJAMIN R. PADGETT,

Examiners.

L. A. SEBASTIAN, Assistant Examiner.

